Preparation

In a kettle of salted boiling water, cook the cauliflower florets for 3 to 4 minutes, or until tender. Drain cauliflower, and plunge into ice cold water to stop the cooking. Drain cauliflower. Pat dry, and transfer to a buttered 2-quart baking dish.
Preheat oven to 350 degrees. In a saucepan, cook the onion in 3 tablespoons of butter over moderate low heat, stirring until it is softened. Stir in the flour and cook the roux over low heat, stirring, for 3 minutes. Add milk and whisk over moderate heat until the sauce thickens. Simmer the sauce for 10 minutes. Season with salt, pepper and grated nutmeg. Pour the sauce over cauliflower. Sprinkle the cheese over the sauce. Pour butter over cheese. Bake until sauce in golden brown, 15 to 20 minutes
cauliflower with cheddar sauce:
A variation of this recipe uses the cream sauce with the addition of 1 1/2 cups grated cheddar cheese, and dry breadcrumbs sprinkled over the top of cauliflower.